1. Field of the Invention
The present invention relates to an ignition apparatus for controlling ignition of an internal combustion engine mainly utilized in a vehicle.
2. Description of the Related Art
In recent years, the issues such as environment preservation and inflammable fuel-air mixture depletion have been raised; measures for these issues are urgently required also in the automobile industry. The measures include, as an example, ultra-lean-combustion (sometimes referred to as stratified-lean-combustion) operation of an internal combustion engine that utilizes a stratified air-fuel mixture. However, in the stratified lean combustion, the distribution of inflammable fuel-air mixtures may vary; therefore, an ignition apparatus capable of absorbing this variation is required. Accordingly, in order to reduce the variation in the distribution of inflammable fuel-air mixtures in the stratified lean combustion, ignition apparatuses disclosed in Patent Documents 1 and 2 have been proposed.
In an ignition apparatus disclosed in Patent Document 1, by use of a capacitive discharging method, a dielectric breakdown is produced between the electrodes of an ignition plug, and after the dielectric breakdown between the electrodes through the capacitive discharging method, an AC spark discharge is continuously produced between the electrodes of the ignition plug through an inductive discharging method. The inductive discharging method is a discharging method in which energy is continually supplied from a coil in which the energy is preliminarily accumulated to the primary coil of an ignition coil device so that an AC spark discharge is continuously produced between the electrodes of an ignition plug. It is alleged that because the conventional ignition apparatus configured in such a manner makes it possible to continue a spark discharge for a long period, a great number of temporal igniting opportunities can be provided and hence the variation in the distribution of inflammable fuel-air mixtures can be absorbed.
A conventional ignition apparatus disclosed in Patent Document 2 is provided with an ignition plug that produces a spark discharge in a combustion chamber and a microwave generation apparatus that supplies energy to the spark discharge produced in the ignition plug. It is alleged that because the conventional ignition apparatus makes it possible to form larger discharge plasma, a great number of spatial igniting opportunities can be provided and hence the variation in the distribution of inflammable fuel-air mixtures can be absorbed.